1. Field of the Invention
The present information relating to providing information affecting mobility to a communications device. In particular, the present invention relates to providing from a transceiver device of a communication system mobility control information relating to neighbor transceiver devices of the communication system.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. Communication systems providing wireless communication for user equipment are known. An example of the wireless systems is a cellular communication system, such as the Global System for Mobile communications (GSM). Another example is the wireless local area network (WLAN).
Communication systems may provide both circuit-switched and packet-switched connectivity. As an example, the GSM system is circuit-switched, but packet-switched connectivity and information transfer can be provided therein by supporting General Packet Radio Service (GPRS). The support for GRPS may be provided, for example, by providing a set of specific GRPS support nodes in a GSM system. In the following the GSM/GPRS system is often used as an example of a communication system.
In a communication system transmission resources are typically arranged into channels. Channels may be common, shared or dedicated depending on whether they are used by all, some or one communications device communicating via a specific cell of the GSM system. Typically there are common control channels at least for providing basic system information about the cell, for setting up connections and for carrying out basic procedures in the GSM system, the basic procedures relating to, for example, mobility management. Typically all communications devices listen to at least one broadcast control channel providing system information.
A communications device communicating with a GSM system (or other communication system supporting mobility) typically needs information about the cell or cells it is currently using for communications and about the neighbor cells. When the quality or strength of the signals the communications devices receives from the communication system changes, the communications device may need to change the cell or cells it uses for communications. Information about the neighbor cells is needed in deciding which cell or cells to use. A communications device may determine and decide itself, which cell or cells to use (this concept is called autonomous mobility), or the communication system may order or instruct a communications device to use certain cell or cells. Change of cells may be called, for example, a cell reselection or a handover. Cell reselection in GSM system typically refers to the case where the communications device autonomously switches between the cells, based on the radio conditions (such as received signal level of serving and neighbour cells) and specific parameters set by the network. Handover in GSM system refers to the case where the network commands the communications device to switch the cell based on measurements results sent by the communications device, typically when there is a circuit-switched connection (such as a speech call) call ongoing.
In current mobility in GSM a communications device (mobile station MS) is required to have knowledge of its neighbor cells and their system parameters in order to be able to utilize those parameters in autonomous mobility. There are currently two approaches how the MS can obtain this information. A first approach is that the MS retrieves the neighbor cell parameters by listening to or communicating using common control channels (especially Broadcast Control Channel, BCCH) of the neighbor cells. A second approach is that the neighbor cell parameters are provided by the GSM network to MS either by sending this information directly to the MS (for example, in a Packet Measurement Order message or in a Packet Cell Change Order) or by scheduling it on a packet broadcast channel PBCCH which is read by the MS.
A mobile station in GSM/GPRS system has at least the following modes. A packet transfer mode, where the MS has one or more active packet data connections called a Temporary Block Flows (TBFs). A packet idle mode with continuous reception (Idle non-DRX), where the MS is prepared to quickly receive all scheduled downlink TBF establishments following to packet data transmission from the GSM/GPRS system to the mobile station. A packet idle mode with discontinuous reception (Idle DRX) where only paging blocks are received.
The first approach for the MS to obtain neighbor cell parameters, which is most common and where the MS autonomously reads the parameters from the signals sent by the neighbor cells according to specified rules, has at least one severe drawback. As the reading of the parameters is not limited to be performed in Idle DRX mode, the MS (when supporting GPRS) is also required to read the parameters while having an active TBF (Packet Transfer/Packet Switched connection) and while being in the Idle non-DRX mode. As the parameters to be read from the neighbor cells are physically transmitted on a different cell/frequency, the MS has to leave the current cell/frequency, tune to the new cell/frequency, in order to receive the actual information. This means that while the MS is receiving the information from the other cell/frequency, the information sent on the serving cell and meant for the MS, will be missed by the MS and the information lost. This information, which can be lost, may be normal data, information for data transmission permission scheduling (Uplink State Flag, USF), changes to current TBF configuration (if during TBF), and a paging message or establishment command for a new TBF (if during idle non-DRX).
A problem in the current situation in GSM/GRPS system is that due the MS may read neighbor cell system information parameters affecting change of cells, to be used in MS autonomous mobility at such time instances that the MS will/may at the same time loose valuable information sent to it.
This same problem also occurs within the provision of broadcast-nature information to several users, such as the Multimedia Broadcast/Multicast Service (MBMS). In this case, though, the problem is even worse as the data is supposed to be received by several mobile stations. The one-to-many (or point-to-multipoint) characteristics of the MBMS service where received data acknowledgments or data retransmissions may not always be used or are ineffective in terms of radio resource usage, together with unsynchronized (determined by individual mobile stations at arbitrary time instants depending on their timing and required information) interruptions in the data reception results in severe difficulties in the broadcast data provision and degraded user experience.
As the GSM/GPRS network is not aware of when the MS schedules the reading of the neighbor cell parameters and therefore the MS—each time MS acquires the required data—will miss the information/data sent from the GSM/GPRS network to the MS. The lost information is currently handled through re-transmission of the information, whenever applicable. In GPRS, this is only possible in Radio Link control (RLC) acknowledged mode, which may not be suitable for streaming/real-time type of Quality of Service (QoS) connections. In these cases where the other mode called RLC unacknowledged mode is used, data is lost during those periods where the MS acquires information from neighbor cells.
It is appreciated that although problems relating to GSM/GRPS and MBMS service are discussed in detail above, same difficulties may arise in other communication systems and in connection with other services. For example, the same problem identically applies to EGPRS systems, where the GSM system is provided with EDGE (Enhanced Data for GSM Evolution) support.
The aim of the present invention is to address at least some of the problems discussed above.